This invention relates in general to hydraulic systems and deals more particularly with an improved passive hydraulic resistance or damping system of a type which operates in response to an externally applied force to provide controlled resistance to the force. While the hydraulic damping system of the present invention may be useful for many purposes, it is particularly adapted for use in an exercising machine or the like to provide controlled resistance to movement of a member, such as a lever which is manually moved in the performance of an exercising program.
Heretofore various types of closed hyraulic systems have been used in such exercising apparatus. Such hydraulic systems usually include a reservoir or a hydraulic fluid accumulator for receiving hydraulic fluid which is recirculated through the system. It is generally desirable that an exercising machine provide consistently uniform resistive response to specific energy input, however, seal leakage resulting in loss of hydraulic fluid has proven particularly troublesome in such systems. The occurrence of such seal leakage alters the response of the hydraulic system and results in corresponding change in the response of the exercising machine to a specific energy input. Further, when such leakage occurs, hydraulic fluid which escapes from the system must be replenished. Seal replacement often may be required to correct the problem. Further, escape of hydraulic fluid from the system to the surrounding environment is generally undesirable.
Accordingly, it is the general aim of the present invention to provide an improved passive hydraulic resistance system which overcomes the aforesaid problems and which may be regulated to provide controlled response over a wide range of force input conditions.